sql - 多实例的数据库查询

Question

我有一个所有美国邮政编码及其对应的州和国会选区的数据库表，如下所示。

id | zipcode | state_abbr | district
 1     30080      GA           1
 2     30080      TN           2

我需要一个查询，该查询将返回显示在多个州的任何邮政编码。我怎样才能做到这一点？

Answer 1

SELECT zipcode 
FROM (
       SELECT zipcode 
       FROM temp
       GROUP BY zipcode, state_abbr 
     ) AS t 
GROUP BY zipcode 
HAVING COUNT(*) > 1

Answer 2

试试这个 sql。

SQL小提琴

MySQL 5.5.30 架构设置：

CREATE TABLE Table1
    (`id` int, `zipcode` int, `state_abbr` varchar(2), `district` int)
;

INSERT INTO Table1
    (`id`, `zipcode`, `state_abbr`, `district`)
VALUES
    (1, 30080, 'GA', 1),
    (2, 30080, 'TN', 2)
;

查询 1：

select zipcode
from Table1
group by zipcode
having count(zipcode)>1

结果：

| ZIPCODE |
-----------
|   30080 |

Answer 3

SELECT DISTINCT x.zipcode 
  FROM zipcode x 
  JOIN zipcode y 
    ON y.zipcode = x.zipcode 
   AND y.id < x.id;